One of the key sources in finding the location of the bridge where the accident that nearly cost Thomas KINGHORN his life took place has been a book called The Manchester and Glasgow Road: Vol 2 by Charles George Harper. Published by Chapman & Hall Ltd, London in 1907 it is now available for download on Internet Archive.
Chapter 34 of the book describes the road leading up to the bridge, albeit from the opposite direction from which the mail coach was travelling on that fateful night:
The old Glasgow road, that goes up from Moffat past Meikleholmside, and so across Ericstane Muir, is everything a road should not be. It is steep, narrow, exposed, and rugged, and, except as an object-lesson in what our ancestors had to put up with, is a very undesirable route and one in which no one would wish to find himself. It has not even the merit of being picturesque.
Further along the road things did improve, apparently due to the efforts of Thomas Telford:
The road that Telford made continues onward from Beattock in more suave fashion. It follows the glen of Evan Water for nine miles, and the three of them-road, river, and Caledonian Railway-go amicably side by side under the hills, to Beattock Summit and down to Elvanfoot, where the Elvanfoot Inn of other days now stands as a shooting-lodge.
Finally the author describes the bridge where the accident happened:
Elvanfoot Bridge, that carries the road over the Evan (i.e. Avon) Water, looks down upon a pretty scene of rushing stream, boulders, and ferns, or "furruns," as a Scotsman would enunciate the word.
It all sound quite picturesque and the author even includes a sketch of the scene:
Of course if you have read my earlier blog posts (like this one) you will know that on the night of the 25th October 1808 the bridge gave way and sent the mail coach, passengers, driver, guard and horses plummeting into the swollen river below.
The author describes the incident in some detail, although it is not clear where he got his information from, or whether it can be relied on, although the facts do pretty much tie-up with the newspaper reports. This uncertainty is a shame because the book provides an excellent piece of evidence for the exact location of the bridge:
For many years the bridge was not properly mended, funds being scarce on these roads; and the mail, slowing for it, lost five minutes on every journey. The part that fell may still be traced by the shorter lime stalactites hanging from the repaired arch. It is still known as "Broken Bridge," in addition to "Milestone Brig," from the milestone on it, marking the midway distance between Carlisle and Glasgow: "Carlisle 47 1/2 miles. Glasgow 47 miles."
That milestone would be the key to finding the location of the bridge, in the days before detailed Ordnance Survey maps and long before GPS it is a fixed point on a certain route (the road between Glasgow and Carlisle) and even if it wasn’t there now it would probably be shown on earlier maps. If all else failed I could resort to tracing the route on a map and measuring the distance.